1. Field of the Invention
The present invention relates to an air bag apparatus including an air bag cover which is expanded by a bag body toward a vehicle occupant when the vehicle rapidly decelerates, and an insert member embedded in the air bag cover.
2. Description of the Related Art
An air bag apparatus, for example, an air bag apparatus of a type which is mounted on a steering wheel is provided with an insert plate 100 as shown in FIG. 6. The insert plate 100 includes a frame-like insert supporting portion 100A and a pair of insert expanding portions 100B opposed to each other.
As shown in FIG. 7, the insert plate 100 is embedded in an air bag cover 102 by insert molding. The air bag cover 102 is provided with, for example, a substantially H-shaped rupturing portion 104 as seen from the side of an occupant. Thus, the air bag cover 102 is pressed by an expanding bag body (not shown) so as to be ruptured along the rupturing portion 104 and expand when a vehicle decelerates rapidly.
At this time, an expansion center line is positioned at a boundary between the insert expanding portion 100B embedded in the expanding portion 102A of the air bag cover 102 and the insert supporting portion 100A. That is, an edge line P of the insert supporting portion 100A on the occupant side serves as the expansion center line.
Even if the expanding portion 102A of the air bag cover 102 is expanded with the edge line P on the occupant side as an expansion center, an expansion operation of the bag body is not blocked. However, it is desired to enhance expanding performance of the bag body by expanding the expanding portion 102A greater.
In this case, it is possible to satisfy the above requirement by using an insert plate 106 shown in FIG. 8. That is, in the insert plate 106, the height of an insert supporting portion 106A is reduced so as to set an expansion center line Q at a position which is offset on the side opposite the occupant by a predetermined interval away from the edge line P on the side of the occupant side.
However, in case the expansion center line P is simply offset to the expansion center line Q as set forth above, terminals of a rupturing portion 110 are branched when the air bag cover 108 is ruptured, resulting in various rupture lines. That is, there is a problem in that it is impossible to rupture and expand the air bag cover 108 at a predetermined position.